Yoshinobu Tsukada shot a 4-under 68 on Friday to retain a share of the lead after the second round of the Sun Chlorella Classic.
The 42-year-old is tied with Australian Brendan Jones and South Korea's Lee Kyoung Hoon at 9-under-par 135.
Tsukada birdied three straight holes from No. 3 and recovered from his only bogey on the 527-yard, par-5 13th, with a birdie on 17. Lee carded seven birdies in a bogey-free round, while Jones, went on a tear from No. 9, birdying five straight holes.
"My putting has been really good," said Tsukada, who has played in two British Opens but has rarely ever contended for a tour victory. "I don't rightly understand why but they've been falling one after another.
"I wonder what it feels like to win. . ."
Two strokes back are 20-year-old amateur Hideki Matsuyama and 23-year-old Masato Nakanishi, who like Tsukada is seeking his first JGTO tour victory.
Defending champion Yuta Ikeda rebounded from his first-round 75 with a 68 that left him at 1 under in a tie for 44th and eligible to play the weekend rounds at Otaru Country Club.
Sunday's winner will pocket ¥30 million in prize money from the ¥150 million purse.